Calvin Cycle

Definition

The Calvin Cycle is a series of biochemical reactions that occur in the stroma of chloroplasts, where carbon dioxide is converted into glucose using energy from ATP and NADPH produced in the light-dependent reactions of photosynthesis. This cycle is crucial for synthesizing organic compounds, enabling plants to store energy and provide food for themselves and other organisms.

5 Must Know Facts For Your Next Test

1. The Calvin Cycle consists of three main stages: carbon fixation, reduction, and regeneration of ribulose bisphosphate (RuBP).
2. This cycle does not require light directly but relies on products from the light-dependent reactions for energy.
3. The primary product of the Calvin Cycle is glyceraldehyde-3-phosphate (G3P), which can be converted into glucose and other carbohydrates.
4. RuBisCO is one of the most abundant enzymes on Earth and is crucial for fixing carbon dioxide during the first step of the cycle.
5. The Calvin Cycle can occur both during the day and at night as long as there are sufficient amounts of ATP and NADPH available.

Review Questions

• How does the Calvin Cycle utilize ATP and NADPH produced in the light-dependent reactions?
  • The Calvin Cycle uses ATP and NADPH generated from the light-dependent reactions to convert carbon dioxide into glucose. ATP provides the necessary energy to drive the reactions, while NADPH supplies high-energy electrons needed for reducing 3-phosphoglycerate into glyceraldehyde-3-phosphate (G3P). This interdependence illustrates how both stages of photosynthesis work together to produce carbohydrates.
• Evaluate the significance of RuBisCO in the Calvin Cycle and its impact on global carbon cycling.
  • RuBisCO plays a crucial role in the Calvin Cycle as it catalyzes the fixation of carbon dioxide, making it an essential enzyme for photosynthesis. By converting atmospheric CO2 into organic molecules, RuBisCO significantly influences global carbon cycling and climate regulation. Its efficiency and abundance directly affect plant growth and productivity, impacting ecosystems and food supply worldwide.
• Synthesize information about how environmental factors can influence the rate of the Calvin Cycle, including temperature and carbon dioxide concentration.
  • Environmental factors such as temperature and carbon dioxide concentration can greatly influence the rate of the Calvin Cycle. Higher temperatures can increase enzyme activity up to a point, enhancing the cycle's efficiency; however, extreme heat may denature enzymes like RuBisCO. Additionally, increased carbon dioxide concentration generally boosts photosynthesis rates until other factors become limiting. Understanding these influences helps explain how climate change impacts plant growth and agricultural yields.

Related terms

Photosynthesis:

The process by which green plants, algae, and some bacteria convert light energy into chemical energy in the form of glucose, using carbon dioxide and water.

Light-Dependent Reactions: The first stage of photosynthesis, occurring in the thylakoid membranes of chloroplasts, where sunlight is absorbed and converted into chemical energy in the form of ATP and NADPH.

RuBisCO: Ribulose bisphosphate carboxylase/oxygenase, an enzyme that catalyzes the first step of the Calvin Cycle, facilitating the fixation of carbon dioxide into a stable intermediate.